Field of the Invention
The present invention relates to a display apparatus and a substrate used for such a display apparatus, and more particularly, a circuit structure for countermeasures against unnecessary radiation.
Description of the Related Art
A high resolution display panel such as projectors, which performs parallel processing by a plurality of image processing blocks using a high speed operation clock to carry out a composition by one display panel drive circuit, has been used. Using the high speed operation clock and performing the parallel processing of data bases easily generate unnecessary radiation caused by EMI (Electromagnetic Interference). If spread spectrum processing is applied to operation clocks as countermeasures against unnecessary radiation, synchronization among a plurality of image processing blocks is very difficult in the structure driving one display panel using the plurality of the image processing blocks.
For example, as illustrated in FIG. 11A, when modulation characteristics of a spread spectrum in image processing circuits 102 and 103 are not synchronized with each other, differences of clock numbers in a horizontal synchronization signal between the image processing circuits occur. Moreover, as illustrated in FIG. 11B, since differences of clock numbers from each parallel processing block inputted into a display panel drive circuit 104 are large, a large scale FIFO (memory) is required to tolerate the differences of clock numbers.
Japanese Patent Laid-open No. 2008-216606 discloses a synchronization method to solve the above problem by synchronizing a modulation period of a spread spectrum with synchronization signals inputted from outside when spread spectrum processing is applied to operation clocks of an image processing circuit. Additionally, Japanese Patent Laid-open No. 2003-332997 discloses a demodulation method of clocks subjected to spread spectrum processing in respective processing circuit to strictly coincide with timing among the plurality of processing circuits.
However, the method disclosed in Japanese Patent Laid-open No. 2008-216606 may not synchronize among the plurality of image processing blocks (among image processing circuits). Furthermore, the method disclosed in Japanese Patent Laid-open No. 2003-332997 can synchronize among the plurality of image processing blocks, but since a spread spectrum in each image processing block (inside of the image processing circuit) is demodulated, an effect of countermeasures against unnecessary radiation drastically reduces.